Whole systems thinking for sustainable water treatment design
Microbial fuel cell (MFC) technology could provide a low cost alternative to conventional aerated wastewater treatment, however there has been little comparison between MFC and aeration treatment using real wastewater substrate. This study attempts to directly compare the wastewater treatment efficiency and energy consumption and generation among three reactor systems, a traditional aeration process, a simple submerged MFC configuration, and a control reactor acting similar as natural lagoons. Results showed that all three systems were able to remove>90% of COD, but the aeration used shorter time (8 days) then the MFC (10 days) and control reactor (25 days). Compared to aeration, the MFC showed lower removal efficiency in high COD concentration but much higher efficiency when the COD is low. Only the aeration system showed complete nitrification during the operation, reflected by completed ammonia removal and nitrate accumulation. Suspended solid measurements showed that MFC reduced sludge production by 52-82% as compared to aeration, and it also saved 100% of aeration energy. Furthermore, though not designed for high power generation, the MFC reactor showed a 0.3 Wh/g COD/L or 24 Wh/m3 (wastewater treated) net energy gain in electricity generation. These results demonstrate that MFC technology could be integrated into wastewater infrastructure to meet effluent quality and save operational cost.The high cost and life-cycle impact of electrode materials is one major barrier to the large scale application of microbial fuel cells (MFC). We also demonstrate that biomass-derived black carbon (biochar), could be a more cost effective and sustainable alternative to granular activated carbon (GAC) and graphite granule (GG) electrodes. In a comparison study, two biochar materials made from lodgepole pine sawdust pellets (BCp) and lodgepole pine woodchips (BCc), gassified at a highest heat temperature (HHT) of 1000�C under a heating rate of 16�C/min, showed a satisfactory power density of 532 � 18 mW m-2 and 457 � 20 mW/m-2 respectively, compared to GAC with 674 � 10 mW m-2 and GG with 566 � 5 mW m-2 (normalized to cathode projected surface area), as an anode material in a two-chamber MFC. BCc and BCp had BET-N2 surface area measurements of 429 cm2 g-1 and 470 cm2 g-1 respectively, lower than industrial GAC with 1248 cm2 g-1 but several orders of magnitude higher that GG with 0.44 cm2 g-1. BCc and BCp had a lower surface resistance of 3�1Ω mm-1 and 6�1Ω mm-1 than 8�2Ω mm-1 for GAC, but higher that GG with 0.4�0.5Ω mm-1. We also investigated the life-cycle impact and estimated cost of biochar as an electrode material. Although there is no well-established market price for biochar, conservative estimates place the costs around 51-356 US$/tonne, up to ten times cheaper that GAC (500-2500 US$/tonne) and GGs (500-800 US$/tonne) with significantly greater life-cycle advantages.
Book contributor Auraria Library
Collection auraria; additional_collections